The background of this Invention lies on the one hand in the efforts currently being made to reduce or eliminate dumping in order to reduce the sources of environmental pollution of industrial origin, and on the other hand, in the repeated attempts to utilize starting products as completely as possible, all within the framework of several procedural guidelines which also make it possible to reduce energy consumption.
As is well known, the agriculture/food industries have a strong impact, both with respect to the BOD.sub.5 of their waste and with respect to materials in suspension, and among these, those relating to grape and raisin juices have a markedly high content, to the point of requiring a DBO.sub.5 higher than 1,400 mg/l of sugared solution adsorbed in the sludges or argols, together with some materials in suspension in concentrations higher than 600 mg/l, also with reference to absorbed solution. To these one must add the requirements of the argols themselves, which are even higher due to their specific nature as organic acids and salts of medium molecular weight, which results in occasional resorting to fradulent dumping of waste in order to avoid the cost of treatment.
In conventional processes, the obtaining of concentrates of grapes, raisins, and other fruits is carried out by subjecting the initial juice to successive concentrations by evaporation to obtain a final syrup which has a concentration of approximately 70.degree. Brix.
In the preceding process, however, a large number of organic salts or acids having two to nine carbon atoms are precipitated, so that these are separated by means of successive static decantings, with long durations, which entails the initial decanting of another series of substances which are more or less colloidal, which, in addition to increasing the degree of impurities in the argols, making it impossible to utilize them subsequently, reduces the later stability of the juices, as they are separated from them.
What is more, however, the particle size of these sludges produces high levels of adsorption in the sugared solution, resulting in a loss of yield.
Under these conditions, utilization of the argols for other purposes is impossible.
To sum up, the drawbacks of the conventional process are as follows:
a) The nature of the concentrated syrups, together with their high viscosity, makes the decanting process slower and deficient, because it may be incomplete in relation to the argols, while, given the slowness of the process, undesired precipitation of natural stabilizing compounds, such as gelatins or pectins which are initially contained in the syrup in a colloid state, may occur.
b) Separation of phases is difficult because an interface zone, which must be incorporated into the sludge, is always produced, and this must be eliminated if one wishes to guarantee the quality of the final juice.
c) The massive incorporation of sugars, or in a smaller proportion polysaccharides such as gelatins, into argols limits the possibility of their use, both due to their inherent composition and due to the problems of storage and transport in view of the risk of proliferation of fermentation processes. This makes it necessary to destroy the argol, causing an increase in costs, and what is worse, direct dumping with the ecological impact we have discussed above.
The method carried out to date to recover sugars adsorbed in the sludges and to reduce, if not completely avoid, contamination of these sludges, consists of a series of successive washings of the sludges or argols with water, such that the adsorbed sugar solution progressively decreases in concentration as the number of stages of washing increases. Naturally, during these washings, parts of the organic compounds contained in the argols may once again dissolve, with the result that it is necessary to use cold or chilled water, with the additional consumption of energy that this requires, in order to reduce the solubility of the sludges. In this manner, the more efficient the separation of sugars by washing, the more organic acids and salts, oxalates, bioxalates, tartrates, bitartrates, and citrates return to the sugared solution. On the other hand, the wash water which, once it has been separated by decanting, has widely varying concentrations between 2.degree. and 30.degree. Brix, must be concentrated to a level of 60.degree.-70.degree. Brix for reincorporation in the juice cycle, which entails a new and high consumption of energy. This explains the fact that this water purification stage is frequently dispensed with, taking on the risk of generating unusable argols. The composition of unpurified argols or argols washed with one or two steps is as follows:
Sugar: 30-50% PA1 Water: 18-25% PA1 Other substances: 30-40%
That means, the proportion of sugars to actual sludges may reach a level of 1:1, which gives an idea of both the losses and the degree of sugar contamination of the argols themselves.
The procedure which is the object of our Invention overcomes all of the difficulties described by improving yields of recovery of sugar, reducing the presence of sugars in argols, reducing the time of decanting of same, and eliminating the processes of washing and the resulting recovery of these sugars, which in turn reduces the energy consumption of the process.